1. Technical Field
The present invention relates to a semiconductor device and a current amount control method.
2. Related Art
In processing circuits, such as logic circuits, that are mounted to semiconductor chips (semiconductor integrated circuits), direct application of a semiconductor chip power source voltage is sometimes not possible due to a decrease in tolerable voltage accompanying miniaturization of the transistors employed. In such cases, a constant voltage device is mounted to the semiconductor chip, and a predetermined voltage is generated using the constant voltage device and supplied to the logic circuit. As an example of such a constant voltage device, Japanese Patent Application Laid-Open (JP-A) No. 2008-17566 describes a power generation circuit with an output connected to an externally attached capacitor element that acts as a decoupling capacitor.
Recently, due to demands for cost reduction and miniaturization of mounted boards, there is a call for decoupling capacitors to be internally provided to semiconductor chips, rather than externally connected. Decoupling capacitors generally have a smaller capacity when internally provided than when externally connected. Constant voltage devices are accordingly heavily affected by a voltage drop with respect to the potential of an original output voltage, that occurs due to the load current from driving the logic circuit.
To solve this issue, the response time of a constant voltage device is shortened by increasing the constant voltage device drive current when capacitor elements are internally provided, compared to when capacitor elements are externally connected. An example of a method enabling current amount to be varied is described in, for example, JP-A No. 2007-228357, in which the current amount of a current generated by a current mirror circuit can be varied.
When capacitor elements are internally provided to semiconductor chips, there is an issue of increased current consumption due to the increase in the current amount of the constant voltage device, as described above. As a result, externally connected capacitor elements are employed when current consumption takes precedence over mounted board miniaturization (when current consumption is suppressed).
Constant voltage devices that are compatible whether or not externally connected capacitor elements are present are therefore desirable, since whether or not externally connected capacitor elements are employed is determined by, for example, user preference. However, in the technology of JP-A No. 2008-17566 and JP-A No. 2007-228357, the current amount of the constant voltage device drive current does not change according to whether or not externally connected capacitor elements are present.